Each information processing apparatus judges a busy flag of a first port thereof based on a result of comparison of a busy level of the first port and a busy level of a second port of another information processing apparatus. A monitoring apparatus determines from among the information processing apparatuses, a first information processing apparatus and a second information processing apparatus, based on the results of judgment by the information processing apparatuses. An L2 switch changes to the second information processing apparatus, a destination of a frame whose destination is the first information processing apparatus and changes to the first information processing apparatus, a transmission source of the frame whose transmission source is the second information processing apparatus.